High resistivity liquid/solid resistor

ABSTRACT

A compact stable liquid-solid resistor having a large resistance to length ratio is disclosed. The range of resistivities is exceptionally wide because liquid and solid dielectrics are employed together.

United States Patent Hadermann et al.

1 1 Oct. 29, 1974 HIGH RESlSTlVlTY LIQUID/SOLID RESISTOR inventors: Albert F. Hadermann, ljamsville,

Md.; Paul F. Waters, Washington, DC; Jung W00 W00, Arlington,

Assignee: Applied Physical Chemistry lnc.,

ljamsville, Md.

Filed: June 1, 1973 Appl. No.: 366,009

US. Cl 338/222, 252/500, 338/51,

338/224 Int. Cl H0lc 11/00 Field of Search 338/222, 223, 224, 54,

Primary Examiner-E. A. Goldberg Attorney, Agent, or Firm.loseph P. Nigon [57] ABSTRACT A compact stable liquid-solid resistor having a large resistance to length ratio is disclosed. The range of resistivities is exceptionally wide because liquid and solid dielectrics are employed together.

3 Claims, 7 Drawing Figures IIIIII IIIIIIII IIIIIIIIIIIIIIII m HIGH RESISTIVITY LIQUID/SOLID RESISTOR BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION The present invention is directed to a liquid-solid resistor which is compact and stable. The range of resistivities covered by the invention is exceptionally wide because liquid and solid dielectrics are employed in conjunction. The resistors of the present invention may be manufactured with a large resistance to length ratio.

The present invention has for its object a liquid-solid resistor having a resistivity which is based on specific resistivity of the order ofS X It) ohm-cm, or larger, depending on the mean, or effective pore size of the solid dielectric and the specific resistivity of the liquid dielectric. A specific resistivity of 5 X l ohm-cm was obtained for a porous plug of gamma aluminaof mean particle size of less than 0.] micron and isopropanol. The resistance value for a particular resistor of cross sectional area, s, and plug thickness, r, is given by:

The specific resistivity of the dielectric-saturated porous plug depends on the composition of the solid dielectric. the liquid dielectric and the mean pore size. The general equation for the resistance of liquid solid resistors is:

where p is the specific resistance of the resistor.

A liquid-solid resistor has certain advantages over pure solid and pure liquid resistors. These advantages are:

l. Great stability of the porous region to electrical breakdown, eg, a dielectric strength greater than 100 kV/cm for systems comprised of gamma alumina and isopropanol.

2. Extremely small size, e.g., a X l0 ohm resistor for use in the 100 IN region measures one cm in diameter by one cm in length. The size of the entire liquidsolid resistor is one cm in diameter by 3 cm in length.

3. Ease of renewal of the liquid if required.

4. Much greater control of the resistance than is possible in the case of pure liquid or pure solid resistors since the additional resistance determining parameters of the resistivity of the liquid saturated porous region depend on the specific resistivities of the liquid and solid and on the mean pore size of the solid and the ex tent to which the solid is compressed prior to satura- IIOII.

5. Very effective removal of heat by employing the phenomenon of electro-osmosis to circulate the liquid dielectric through a heat exchanger.

6. The induction of deviation from ohmic behavior by introducing small quantities of weak electrolytes, e.g., water, into an alcohol, e.g., isopropanol. Linear and n0n-linear resistors can be obtained in the same resistivity range. I

The concept of the liquid'solid resistance includes the use of non-polar as well as polar liquids. Thus, it is possible to employ liquids with specific resistivities greater than or less than l0" ohm-cm. Examples of suitable liquids include isopropanol, ligroin, cyclohexane, octane, dioxane, ethanol. l-hexanol, acetone, 2- pentanone, amyl acetate. etc., or any other physically and chemically compatible substance which is a liquid under the conditions of temperature and pressure experienced by the resistor of this invention.

Typically, isopropanol has a specific resistance of 2.9 X 10 ohm-cm at 25 C when used in the present invention. Liquids having high or low dielectric constants may be used. The porous solid can be comprised of alumina, silica, powered glass, quartz, sulfur, titanium oxide, barium sulfate, organic polymers, etc., or any organic or inorganic substance which has a higher spe cific resistance than the liquid employed in the system constituting the resistor. It is not necessary to add an organic acid, as is the case in the prior art, in order to increase the ionizing property of the liquids which are employed in the present invention. The auto-ionization of isopropanol is sufficient to supply the necessary current carriers. The entire liquid content of the liquidsolid resistance serves as a potential ion reservoir for the device, thus providing inherent long-term stability. The geometry of the liquid-solid system may be varied according to equation I providing a coverage from at least IO to 10" ohm-cm.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a liquid-solid resistor in accordance with the invention.

FIG. 2 is a curve showing the behavior of a typical linear resistor.

FIG. 3 is a curve showing the behavior of a typical non-linear resistor containing a weak electrolyte, e.g., water, in the liquid-solid system.

FIG. 4 shows a liquid-solid resistor leading to a maximization of the extent of the porous region of the system.

FIG. 5 shows a geometric arrangement of the liquidsolid resistor to maximize the surface to length ratio in equation I.

FIG. 7 shows a self-cooled liquid-solid resistor employing the phenomenon of electro-osmosis t0 engender fluid motion from the high-resistance region of the invention to a heat exchanger.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring in detail to the accompanying FIGS. 1, 2, 3, 4, 5, 6 and 7, the liquid-solid resistance device which is shown in FIG. 1 is constituted by a resistance liquid, I, contained in a sealed insulating housing, 2, having an internal diameter of the order of 10 mm and a length of the order of 30 mm. The solid dielectric powder, 3, is held in place by the porous plates, 4, two platinum electrodes, 5, are enclosed in potting, 6, and extend to the body of the resistor. Due to the small size of the resistor. the input wires should be very well insulated or a discharge through the air may occur.

HO. 2 shows the shape of the current vs applied potential curve for a system consisting of gamma alumina and isopropanol which does not contain any added weak electrolyte. The shape of the current vs potential curve shows that Ohms law is obeyed. Linear liquidsolid resistors may be employed wherever a highvoltage. high-resistance ohmic resistor is required.

FIG. 3 shows the shape of the current vs applied potential curve for a system consisting of gamma alumina and isopropanol which contains water. The shape of the current vs potential curve shows that ohms law is not obeyed. Non-linear liquid-solid resistances may be employed wherever a non-ohmic resistor is required.

SPECIFIC DATA ON FIGS. 2 AND 3 FIG. 2. This system was comprised of 0.6 grams of gamma alumina of a mean particle size of 0.l micron and was activated at 53l C and 6 X 10 mm of mercury pressure for 3 hours. The isopropanol contained less than parts per million of water.

FIG. 3. This system was comprised of 0.5 grams of gamma alumina of a mean particle size of 0.1 micron and was activated by heating in air at 154 C for 18 hours. The isopropanol contained less than l0 parts per million of water. The non-linearity is ascribed to the water originally present on the alumina surface.

FIG. 4 shows a liquidsolid resistance design on maximizing the quantity of the porous region. 3. between the platinum electrodes, 5. and contained in the insulating housing 2. This approach leads to a more compact design than that shown in FIG. I. The lead-in wires must be potted in a good insulator such as silicone. 6. in order to guard against corona.

FIG. 5 shows a geometric arrangement of the contents of the liquid-solid resistor which maximizes the current path through the liquid-solid region. 3. The porous region is placed between a central platinum electrode. 7. and an electrode. 8. concentric with the inside of the insulating housing 2.

A platinum input disc. 9. is connected to the concentric platinum electrode. The input disc is connected to the lead-in electrode. 10. which is potted, 6.

FIG. 6 is a voltage divider employing a liquidsolid resistance. The insulating housing. 2. is filled with the liquid-solid resistance. 3. A potential difference is applied across electrodes. 5, which are potted. 6. and fractions of this potential difference may be tapped at electrodes I]. I2, and 13.

FIG. 7 shows a liquid-solid resistor which is cooled by electro-osmotically engendered fluid motion. When a difference of potential is applied to electrodes. 5. current passes through the porous region, 3, located between the porous supports, 4. The solid within region. 3, is electro-osmotically active with the liquid. e.g., gamma alumina with isopropanol and a pressure gradient will be established in the direction going from the anode to the cathode. The fluid in electrode compartment, 14, will flow through the porous support. 15. supported by member 50, and through the channel. 16. into the heat sink. 17. The region within the channel. 16, is filled with a powdered insulator. e.g.. sulfur. which is electroosmotically inactive in conjunction with the liquid. Thus. channel. 16. is provided with a high electrical resistivity without interfering with the flow of the fluid from electrode compartment. 14. to electrode compartment. 1. As larger amounts of electrical power are applied to electrodes. 5, the electroosmotic flow rate increases and the rate of heat transfer to the heat sink. 17, increases. This design is for a very compact high-voltage, high-power resistor which is effectively cooled by electro-osmotically driven heat transfer.

What is claimed is:

l. A resistor having a specific restivity of at least 5 X lO ohm centimeters comprising: a body of electrically insulating material having first and second end portions, and containing a high resistivity liquid-solid mixture which is stable in time. wherein said liquid-solid .resistance comprises a polar or non-polar liquid selected from the group consisting of isopropanol. ligroin. cyclohexane. octane. dioxane. ethanol, l hexanol. acetone. 2 pentanone and amyl acetate. and a powdered solid dielectric having a particle size of about 0. l micron selected from the group consisting of alumina. silica. powdered glass. quartz. sulfur. titanium oxide. barium sulfate and organic polymers. first and second terminals formed on respective opposite ends of said body. each including a lead wire secured to a respective end of said body and extending into the inner portion containing the polar or non-polar liquid-powdered solid dielectric mixture.

2. The resistor according to claim 1 wherein the body of said resistor comprises at least three compartments. and wherein said compartments are separated by a ceramic membrane.

3. The resistor according to claim 1 wherein the powdered solid dielectric is alumina having a mean particle size of 0.l micron and the non-polar liquid is isopropanol. 

1. A RESISTOR HAVING A SPECIFIC RESTIVITY OF AT LEAST 5X10$ OHM CENTIMETERS COMPRISING: A BODY OF ELECTRICALLY INSULATING MATERIAL HAVING FIRST AND SECOND END PORTIONS, AND CONTAINING A HIGH RESISTIVITY LIQUID-SOLID MIXTURE WHICH IS STABLE IN TIME, WHEREIN SAID LIQUID-SOLID RESISTANCE COMPRISES A POLAR OR NONPOLAR LIQUID SELECTED FROM THE GROUP CONSISTING OF ISOPROPANOL, LIGROIN, CYCLOHEXANE, OCTANE, DIOXANE, ETHANOL, 1 HEXANOL, ACETONE, 2 PENTANONE AND AMYL ACETATE, AND A POWDERED SOLID DIELECTRIC HAVING A PARTICLE SIZE OF ABOUT 0.1 MICRON SELECTED FROM THE GROUP CONSISTING OF ALUMINA, SILICA, POWDERED GLASS, QUARTZ, SULFUR, TITANIUM OXIDE, BARIUM SULFATE AND ORGANIC POLYMERS, FIRST AND SECOND TERMINALS FORMED ON RESPECTIVE OPPOSITE ENDS OF SAID BODY, EACH INCLUDING A LEAD WIRE SECURED TO A RESPECTIVE END OF SAID BODY AND EXTENDING INTO THE INNER PORTION CONTAINING THE POLAR OR NON-POLAR LIQUID-POWDERED SOLID DIELECTRIC MIXTURE.
 2. The resistor according to claim 1 wherein the body of said resistor comprises at least three compartments, and wherein said compartments are separated by a ceramic membrane.
 3. The resistor according to claim 1 wherein the powdered solid dielectric is alumina having a mean particle size of 0.1 micron and the non-polar liquid is isopropanol. 